1. Field of the Invention
The present invention relates to a current drive device that supplies drive currents to an apparatus to be driven such as an organic electroluminescence (EL) display panel, for example.
2. Description of the Prior Art
In organic EL panels and the like, for example, a current drive device that supplies currents corresponding to image data for respective pixels is used. As shown in FIG. 14 of Japanese Laid-Open Patent Publication No. 2005-49632, for example, this type of current drive device outputs drive currents corresponding to image data by allowing or blocking flows of mirror currents to current sources 1112 (n-type transistor) with corresponding switches 1115.
The above publication also suggests a technology in which cascode MISFETs 55 are provided, as shown in FIG. 6, to suppress the drain voltage of the current sources 1112 from varying to thereby enhance the precision of the drive currents.
However, even with the provision of the cascode MISFETs 55 as described above, the drain voltage of the current sources 1112 becomes close to the ground voltage (VSS) when the switches 1115 are turned off, and thereafter rises sharply when the switches 1115 are turned on. This variation in drain voltage affects the gate voltage via a gate-drain parasitic capacitance. Therefore, in this case, also, the precision of the drive currents will be degraded.